Evidence for chloride secretion in the intestine of the winter flounder

The effects of a novel antisecretory peptide (CAP) isolated from porcine heart and vasoactive intestinal peptide (VIP) on ion transport were investigated in the winter flounder intestine. Partially purified CAP caused a two- to sixfold increase in the serosa-negative short-circuit current (Isc) with no significant change in tissue conductance. CAP significantly inhibited the serosal-to-mucosal (S-M) unidirectional Cl flux without affecting either Na or Rb transepithelial fluxes. The Isc after the addition of CAP was completely inhibited by 0.1 microM atriopeptin III (AP-3), 10 microM bumetanide, and 100 microM 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP). In contrast to the effects of CAP on Isc, VIP decreased the serosa-negative Isc by 40-60%. VIP stimulated the S-M unidirectional Cl flux without affecting transepithelial Na transport. When food was present in the intestine, the basal Isc was occasionally found to be serosa positive, ranging between 10 and 40 microA/cm2. Treatment of tissues exhibiting serosa-positive currents with VIP resulted in an increase (positive direction) in Isc. Addition of CAP to tissues with a serosa-positive Isc or to tissues pretreated with VIP resulted in a serosa-negative Isc.(ABSTRACT TRUNCATED AT 250 WORDS)